1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method of fabricating the same.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices are driven so as to use the optical anisotropy and polarization characteristics of a liquid crystal material. More particularly, liquid crystal molecules have a definite alignment as a result of their long, thin shapes and are arranged to have initial pre-tilt angles. The alignment direction can be controlled by applying an electric field. Accordingly, variations in an applied electric field influence the alignment of the liquid crystal molecules. Due to optical anisotropy of the liquid crystal molecules, the refraction of incident light depends on the alignment direction of the liquid crystal molecules. Thus, by properly controlling the applied electric field, an image that has a desired brightness can be produced.
FIG. 1A is a perspective view schematically illustrating a related art LCD device, and FIG. 1B is an enlarged view of a thin film transistor T in FIG. 1A. As shown in FIGS. 1A and 1B, the LCD device 51 includes a first substrate 22 and a second substrate 5, which are spaced apart from each other, and a liquid crystal layer 11 (not shown) interposed between the first substrate 22 and second substrate 5. A black matrix 6, a color filter layer 7, and a common electrode 9 are formed on an interior surface of the second substrate 5, which faces the first substrate 22. The color filter layer 7 includes red, green and blue color filters 7a, 7b and 7c, each of which is disposed in an opening of the black matrix 6. The common electrode 9 is transparent and covers the black matrix 6 and the color filters 7a, 7b and 7c. 
A plurality of pixel regions P are defined on an interior surface of the first substrate 22, which faces the second substrate 5. A plurality of gate lines 12 and a plurality of data lines 24 cross each other to define the plurality of pixel regions P. A thin film transistor T is formed adjacent to where the gate and data lines 12 and 24 cross each other. The thin film transistor T includes a gate electrode 30, an active layer 32, a source electrode 34, and a drain electrode 36. The active layer 32 overlaps the gate electrode 32, and the source and drain electrodes 34 and 36 are spaced apart from each other and positioned over the active layer 32. A pixel electrode 17 is formed in each pixel region P and is connected to the drain electrode 36 of the thin film transistor T in each pixel region P. The pixel electrode 17 includes a transparent conductive material having high transmittance, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The thin film transistor T and the pixel electrode 17 of each pixel are arranged in a matrix form. Pulse signals are provided to the gate electrode 30 through the gate line 12, and data signals are provided to the source electrode 34 through the data line 24.
The second substrate 5 including the black matrix 6, the color filter layer 7 and the common electrode 9 is often referred to as a color filter substrate. The first substrate 22 including the gate lines 12, the data lines 24, the thin film transistors T and the pixel electrodes 17 is often referred to as an array substrate.
In the above related art LCD device, various approaches have been researched for achieving wide viewing angles and high brightness. A multi-domain method, a phase compensation method, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, and so on have been researched and developed as methods for achieving wide viewing angles. In the multi-domain method, a pixel is divided into several regions, in which each of the liquid crystal molecules are differently arranged so that each pixel has overall average properties. In the phase compensation method, a phase difference film, which is often referred to as a retardation film, is used to reduce changes in phase difference depending on viewing angles. In the IPS mode, liquid crystal molecules move in a plane substantially parallel to the substrates corresponding to an electric field produced in parallel to the substrate of the LCD device. In the VA mode, liquid crystal molecules having negative dielectric anisotropy are arranged vertically with respect to the substrate when voltage is not applied.
Among the above methods, the VA mode has the additional advantage of fast response time as compared to the twisted nematic (TN) mode, which is widely used in conventional LCD devices. The VA mode has a response time of about 30 ms as compared with the 50 ms of the TN mode, when the transmittance of the LCD device changes from 100% to 50%. Generally, in the VA mode, a vertical alignment material, a liquid crystal material with negative dielectric anisotropy and a negative retardation film are used. Thus, the VA mode has a wide viewing angle, and has a high contrast ratio.
FIG. 2 is a cross-section view illustrating a pixel region of a VA mode LCD device according to the related art. As shown in FIG. 2, a pixel electrode 17 is formed on an interior surface of a first substrate 22, and a black matrix 6, a color filter layer 7 and a common electrode 9 are subsequently formed on an interior surface of a second substrate 5, which is spaced apart from and facing the first substrate 22. A liquid crystal layer 11 is interposed between the first and second substrates 22 and 5. The liquid crystal layer 11 has a negative dielectric anisotropy, and liquid crystal molecules of the liquid crystal layer 11 may be vertically arranged between the first and second substrates 22 and 5.
When a voltage is applied to the pixel electrode 17 and the common electrode 9, an electric field E substantially perpendicular to the substrates 5 and 22 is induced between the pixel electrode 17 and the common electrode 9, and the liquid crystal molecules of the liquid crystal layer 11 are realigned so as to be perpendicular with respect to the direction of the electric field E. At this time, the pixel electrode 17 is partially patterned and has slits S (or holes), and the electric field E is distorted due to the slits S. Thus, multi-domains are formed in one pixel region. Further, a rib is formed on the common electrode 9 at a center portion between the slits S of the pixel electrode 17, and the pixel region may be symmetrically divided so as to have mirrored patterns or the same patterns at upper and lower parts of the pixel electrode 17. Meanwhile, a spacer SP is further formed on the common electrode 9 to maintain a cell gap between the first and second substrates 22 and 5.
FIGS. 3A to 3D are cross-sectional views illustrating a manufacturing method of a color filter substrate for a related art VA mode LCD. As shown in FIG. 3A, a black matrix 6 is formed on a transparent substrate 5 by coating a black resin and then patterning the black resin through a first mask process, or by depositing either chromium (Cr) or chromium oxide (CrOX) and then patterning one of the chromium layers through a first mask process. The black matrix 6 may be in a variety of shapes depending on the structure of an array substrate (not shown). However, the black matrix typically has a lattice shape.
As shown in FIG. 3B, a color filter layer 7 is formed on the substrate 5, including the black matrix 6. The color filter layer 7 includes red, green and blue color filters. The color filter layer 7 may be formed through one of various methods. A pigment dispersion method is widely used for forming the color filter layer 7. In the pigment dispersion method, each color filter can be formed by coating a pigment resin across a surface of the transparent substrate 5 and then patterning the pigment resin through a mask process. Accordingly, the color filter layer 7 having three colors can be formed through a three mask process, such as second, third and fourth mask processes.
As shown in FIG. 3C, a common electrode 9 is formed across the surface of the substrate 5, including the color filter layer 7. Subsequently, a rib R is formed on the common electrode 9 by coating a resin and then patterning the resin through a fifth mask process. As shown in FIG. 3D, a spacer SP having a columnar shape is formed on the substrate 5 by coating a polymer resin and then patterning the polymer resin through a sixth mask process. The spacer SP corresponds to the black matrix 6. The color filter substrate for the VA mode LCD device, including the spacer SP and the rib R, is manufactured using six mask processes. Thus, the color filter substrate for this related art VA mode LCD device has two additional mask processes for the rib and the spacer as compared to a color filter substrate for a related art TN mode LCD device, which is manufactured using four mask processes. Accordingly, manufacturing time and costs are higher for a VA mode LCD, and thus productivity is lower.
To improve productivity, a process for simultaneously forming the rib and the spacer has been proposed. FIGS. 4A to 4C are cross-sectional views illustrating a manufacturing method of another color filter substrate for another related art VA mode LCD device. As shown in FIG. 4A, a black matrix 52 is formed on a transparent substrate 50, on which pixel regions P are defined, by coating a black resin and then patterning the black resin through a first mask process.
As shown in FIG. 4B, a color filter layer is formed on the substrate 50, including the black matrix 52. The color filter layer includes red 54a, green 54b and blue (not shown) color filters. The red, green and blue color filters can be formed through second, third and fourth mask processes, respectively. This masking process yields color filters that overlap each other. For example, the red and green color filters 54a and 54b, are sequentially formed such that they both overlap the black matrix 50 and the green color filter 54b overlaps the red color filter 54a. A subsequent blue color filter (not shown) would overlap the black matrix 50 and both of the red and green color filters 54a and 54b. Accordingly, the combined thickness of the black matrix 52, the red color filter 54a and the green color filter 54b is thicker than a thickness of each of the color filters in the pixel regions P.
As shown in FIG. 4C, a common electrode 56 is formed across a surface of the substrate 50, including the color filter layer. A first rib R1 and a second rib R2 are formed on the common electrode 56 by coating a resin and then patterning it through a fifth mask process. The first rib R1 is disposed over where the green color filter 54b, the red color filter 54a, and the black matrix 52 are sequentially overlapped, and the second rib R2 is disposed in each pixel region P. The first rib R1 together with the overlapped color filters 54a and 54b functions as a spacer, and the second rib R2 is used to form multi domains in one pixel region. A total thickness H of the first rib R1 and the overlapped color filters 54a and 54b may be about 4 μm. Accordingly, a color filter substrate may be manufactured through a five mask process, which is less than the six mask manufacturing processes for a color filter substrate shown in FIGS. 3A to 3D. However, the common electrode 56 in the five mask color filter substrate may be disconnected due to a step coverage (or difference) created by the overlapping color filters on the black matrix.